The apparatus and method of this invention relates to a portable reel system. The system of this invention has been specifically designed for installation and use on supply boats, drillships, and any other vessel (advantageously self-propelled), having sufficient clear-deck area to accommodate the combination of structural assemblies making up the reel pipelaying system described hereunder.
More particularly, the present invention relates to a reel pipelaying system mounted on the clear-deck area to a suitable carrier vessel (preferably self-propelled) so that the carrier vessel, for example, a supply boat, can be used to lay pipelines to and from offshore drilling platforms and/or storage tanks and/or terminal locations and/or sub-sea well completion units. For convenience of description, and since an operational system has been successfully mounted on a supply vessel, reference hereunder will sometimes be made to a supply boat as one specific carrier vessel.
As used in the present description, "supply boats" are sometimes referred to in the offshore oil industry as "supply vessels" and/or "tug/supply vessels"; they are characterized by a generally flat, continuous on-deck cargo-carrying space between the superstructure and the stern and are primarily used for carrying supplies, equipment, and personnel between a shore base and an offshore platform or rig. Supply boats generally have dimensions and cargo capacities within the following ranges:
Length: 170 feet-225 feet
Gross Registered Tonnage (G.R.T.): 450T-1300T
Continuous On-Deck Cargo Space Between Superstructure and Stern: 2300-4800 sq. ft.
On-Deck Cargo Capacity Between Superstructure and Stern: 300-700T
Supply vessels as defined above and as generally referred to in the present description are exemplified in catalogs of the following representative suppliers of such vessels:
(1) Smit-Lloyd:
1977 Catalog of 16 pages, entitled "ANYWHERE, ANYTIME, ANYHOW" with picture of supply boat "Smit-Lloyd 104" on front cover;
(2) Maersk:
1973 Catalog of 12 pages, entitled "Maersk Supply Service/A. P. Moeller" and describing three supply boat types;
(3) Offshore Supply Association, Ltd. (OSA):
1976 Catalog of 8 pages, entitled "Actions Speak Louder Than Words", and bearing legend on back cover: "Printed in West Germany, November 1976".
Another type of carrier vessel for which the reel pipelaying system of this invention may be suitable is the so-called "drill ship"; such vessel is generally a self-propelled ship mounting a drilling tower or rig. The drilling tower may be of the center-line type, in which drilling is done through a well in the center of the ship; an alternative construction has the drilling rig cantilevered over the side of the vessel. Examples of drill ships are shown in Howe, R. J., "The Evolution of Offshore Mobile Drilling Units", Ocean Industry, 1966. Drill ships of either type and having sufficient clear-deck space to mount the combination of elements of the reel pipe-laying system of this invention, may be advantageously used to combine several offshore operations. Specifically, when the drill ship has completed its hole into an oil reserve, the same ship can then lay pipe between the sub-sea well completion and collection point, such as a storage tank.
Historically, the technique of laying undersea fluid-carrying pipelines had its rudimentary beginnings in England in the 1940's. In the summer of 1944, 3" nominal bore steel tubes, electrically flash-welded together, were coiled around floating drums. One end of the pipe was fixed to a terminal point; as the floating drums were towed across the English Channel, the pipe was pulled off the drum. In this manner, pipeline connections were made between the fuel supply depots in England and distribution points on the European continent to support the allied invasion of Europe. (See Blair, J. S., "Operation Pluto: The Hamel Steel Pipelines", Transactions of the Institute of Welding, February 1946.)
The broad concept of reel pipelaying was also disclosed in British Pat. No. 601,103 (Ellis), issued Apr. 28, 1948, wherein it was suggested that lengths of pipe be joined together at the manufacturing plant and coiled onto a drum, mounted on a barge or ship; the loaded barge would then be moved to the desired marine location and the pipe unwound from the drum by fixing one end of the pipe and towing the barge away from the fixed location.
While the concepts described in British Pat. No. 601,103 and those actually used in Operation Pluto were adequate for wartime purposes, no known further development work or commercial use of the technique of laying pipe offshore from reels was carried out after World War II. After a hiatus of about fifteen years, research into the reel pipelaying technique was renewed and was carried on by Gurtler, Hebert & Co., Inc., of New Orleans, La; by 1961, Gurtler, Hebert had sufficiently advanced the reel pipelaying technique to make it a commercially acceptable and viable method of laying pipe in the offshore petroleum industry, able to compete with the traditional stovepiping technique. The first known commercial pipelaying reel barge, called the U-303, was built by Aquatic Contractors and Engineers, Inc., a subsidiary of Gurtler, Hebert, in 1961. The U-303 utilized a large vertical axis reel, permanently mounted on a barge and having horizontally oriented flanges (generally referred to in the trade as a "horizontal reel"). A combined straightener-level winder was employed for spooling pipe onto the reel and for straightening pipe as it was unspooled. The U-303 first laid pipe commercially in September, 1961, in the Gulf of Mexico off the coast of Louisiana and was used successfully during the 1960's to lay several million linear feet of pipe of up to 6" diameter. The U-303 reel pipelaying barge is described in U.S. Pat. No. 3,237,438 (Tesson) and U.S. Pat. No. 3,372,461 (Tesson), both assigned to the assignee of the invention hereof.
The successor to the U-303, currently in use in the Gulf of Mexico and known in the trade as the "Chickasaw", also utilizes a large horizontal reel, permanently mounted to the barge such that it is not readily movable from one carrier vessel to another. Various aspects of "Chickasaw" are described in the following U.S. Patents, all assigned to the assignee of the invention hereof:
______________________________________ Sugasti, et al. No. 3,630,461 Gibson No. 3,641,778 Mott, et al. No. 3,680,432 Key, et al. No. 3,712,100 ______________________________________
Commercial reel pipelaying techniques require the use of certain pipe handling equipment in addition to the reel. Among such pipe handling equipment essential to any commercial reel pipelaying system is a straightener mechanism. This may take the form of a series of rollers or tracks, or any other arrangement which imparts sufficient reverse bending force to the pipe to remove residual curvature so that after unspooling, the pipe will lay substantially straight on the sea bottom. No such pipe-conditioning apparatus was used in Operation Pluto or contemplated by the Ellis British Patent.
U.S. Pat. No. 3,982,402 (Lang, et al.) describes an apparatus for laying pipe from a vertical reel in which the pipe conditioning apparatus is pivotable to adjust the lift-off angle of the pipe relative to the horizontal (e.g., the deck of a ship) as a function of the water depth in which the pipe is being laid. This has distinct commercial advantages, especially where the reel pipelaying system is incorporated into a self-propelled ship, such as that of the present invention, capable of traveling to different job sites, having different pipe size and/or lay depth requirements.
The design of the reel and the entire system of this invention was dictated (1) by the desire to provide a completely self-contained vertical reel pipelaying system which can readily and economically be transferred from one carrier vessel to another, and (2) by the requirements of supply boats which are presently envisioned to be the principal carrier vessels.
Known prior vertical reel systems have had a relatively high center of gravity; using such known systems on a supply boat could increase the overall KG of the boat to a point where it exceeds the stability limits of the vessel.
CG of a reel is substantially co-incident with its rotational axis; thus, the larger the reel diameter at the flanges, the higher will be its CG. The minimum hub diameter, however, is dependent on the largest diameter pipe to be spooled (and vice versa); a reel designed to spool up to 6" diameter pipe must have a larger hub radius than one designed to spool a maximum of 4" diameter pipe.
The reel pipelaying system of this invention, including the reel, the straightener, the pipe guide and their respective support assemblies, was designed to have a low CG while maximizing the amount of pipe which can be spooled for best commercial advantage.